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Glossary · Nouns · A

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TermTypeDefinitionClassificationsUpdated
Acroanesthesianounloss of sensation in the extremitiesverifiedMay 18, 2026
Acrobatnounan athlete who performs acts requiring skill and agility and coordinationverifiedMay 18, 2026
Acrobatic FeatnounMWEa stunt performed by an acrobatverifiedMay 18, 2026
Acrobatic StuntnounMWEa stunt performed by an acrobatverifiedMay 18, 2026
Acrobaticsnounthe performance of stunts while in flight in an aircraftverifiedMay 18, 2026
Acrocarpnouna moss in which the main axis is terminated by the archegonium (and hence the capsule)verifiedMay 18, 2026
Acrocarpous MossnounMWEa moss in which the main axis is terminated by the archegonium (and hence the capsule)verifiedMay 18, 2026
Acrocentric ChromosomenounMWEa chromosome with the centromere near one end so that one chromosomal arm is short and one is longverifiedMay 18, 2026
Acrocephalynouna congenital abnormality of the skullverifiedMay 18, 2026
Acrocyanosisnouncyanosis of the extremitiesverifiedMay 18, 2026
Acrodontnounan animal having teeth consolidated with the summit of the alveolar ridge without socketsverifiedMay 18, 2026
Acrogennounany flowerless plant such as a fern (pteridophyte) or moss (bryophyte) in which growth occurs only at the tip of the main stemverifiedMay 18, 2026
Acroleinnouna pungent colorless unsaturated liquid aldehyde made from propeneverifiedMay 18, 2026
Acromegalianounenlargement of bones of hands and feet and faceverifiedMay 18, 2026
Acromegalynounenlargement of bones of hands and feet and faceverifiedMay 18, 2026
Acromial ProcessnounMWEthe outermost point of the spine of the shoulder bladeverifiedMay 18, 2026
Acromicrianounabnormally small extremities (underdeveloped fingers and toes)verifiedMay 18, 2026
Acromikrianounabnormally small extremities (underdeveloped fingers and toes)verifiedMay 18, 2026
Acromionnounthe outermost point of the spine of the shoulder bladeverifiedMay 18, 2026
Acromphalusnounabnormal protrusion of the navelverifiedMay 18, 2026
Acromyotonianounmyotonia of the extremities onlyverifiedMay 18, 2026
Acronymnouna word formed from the initial letters of the several words in the nameverifiedMay 18, 2026
Acrophobianouna morbid fear of great heightsverifiedMay 18, 2026
Acrophonynounnaming a letter of the alphabet by using a word whose initial sound is the sound represented by that letterverifiedMay 18, 2026
Acropolisnounthe citadel in ancient Greek townsverifiedMay 18, 2026
Acrosomenouna process at the anterior end of a sperm cell that produces enzymes to facilitate penetration of the eggverifiedMay 18, 2026
Acrosticnounverse in which certain letters such as the first in each line form a word or messageverifiedMay 18, 2026
Acrylamidenouna white crystalline amide of propenoic acid can damage the nervous system and is carcinogenic in laboratory animalsverifiedMay 18, 2026
Acrylatenouna salt or ester of propenoic acidverifiedMay 18, 2026
Acrylate ResinnounMWEa glassy thermoplasticverifiedMay 18, 2026
Acrylicnounpolymerized from acrylonitrileverifiedMay 18, 2026
Acrylic AcidnounMWEan unsaturated liquid carboxylic acid used in the manufacture of acrylic resinsverifiedMay 18, 2026
Acrylic FibernounMWEpolymerized from acrylonitrileverifiedMay 18, 2026
Acrylic PaintnounMWEused especially by artistsverifiedMay 18, 2026
Acrylic ResinnounMWEa glassy thermoplasticverifiedMay 18, 2026
Acrylonitrilenouna colorless liquid unsaturated nitrile made from propeneverifiedMay 18, 2026
Acrylonitrile-Butadiene-Styrenenounany of a class of composite plastics used to make car bodies and cases for computers and other appliancesverifiedMay 18, 2026
Act of GodnounMWEa natural and unavoidable catastrophe that interrupts the expected course of eventsverifiedMay 18, 2026
Actinnounone of the proteins into which actomyosin can be splitverifiedMay 18, 2026
Acting OutnounMWEa usually irritating impulsive and uncontrollable outburst by a problem child or a neurotic adultverifiedMay 18, 2026
Actinianounany sea anemone or related animalverifiedMay 18, 2026
Actiniannounany sea anemone or related animalverifiedMay 18, 2026
Actiniariannounany sea anemone or related animalverifiedMay 18, 2026
Actinic DermatitisnounMWEdermatitis caused exposure to sunlightverifiedMay 18, 2026
Actinic KeratosisnounMWEan overgrowth of skin layers resulting from extended exposure to the sunverifiedMay 18, 2026
Actinic RadiationnounMWEelectromagnetic radiation that can produce photochemical reactionsverifiedMay 18, 2026
Actinic RaynounMWEelectromagnetic radiation that can produce photochemical reactionsverifiedMay 18, 2026
Actinidenounany of a series of radioactive elements with atomic numbers 89 through 103verifiedMay 18, 2026
Actinide SeriesnounMWE(chemistry) a series of 15 radioactive elements with increasing atomic numbers from actinium to lawrenciumverifiedMay 18, 2026
Actinismnounthe property of radiation that enables it to produce photochemical effectsverifiedMay 18, 2026
Actiniumnouna radioactive element of the actinide seriesverifiedMay 18, 2026
Actinolitenouna green mineral of the amphibole groupverifiedMay 18, 2026
Actinometernounan instrument for measuring the intensity of electromagnetic radiation (usually by the photochemical effect)verifiedMay 18, 2026
Actinometrynounmeasuring the intensity of electromagnetic radiation (especially of the sun's rays)verifiedMay 18, 2026
Actinomycesnounsoil-inhabiting saprophytes and disease-producing plant and animal parasitesverifiedMay 18, 2026
Actinomycetenounany bacteria (some of which are pathogenic for humans and animals) belonging to the order ActinomycetalesverifiedMay 18, 2026
Actinomycinnounany of various red antibiotics isolated from soil bacteriaverifiedMay 18, 2026
Actinomycosisnoundisease of cattle that can be transmitted to humansverifiedMay 18, 2026
Actinomyxidiannounparasites of wormsverifiedMay 18, 2026
Actinonnounany of a series of radioactive elements with atomic numbers 89 through 103verifiedMay 18, 2026
Actinopodnounprotozoa having stiff rodlike radiating pseudopodsverifiedMay 18, 2026
Actinotherapynoun(medicine) the treatment of disease (especially cancer) by exposure to a radioactive substanceverifiedMay 18, 2026
Actinozoannounsessile marine coelenterates including solitary and colonial polypsverifiedMay 18, 2026
actionnounThe process or fact of doing something; a thing done.ProcessMay 9, 2026
Action at LawnounMWEa judicial proceeding brought by one party against anotherverifiedMay 18, 2026
action itemnounMWEA documented event, task or action that needs to take place. Action items are discreet units that can be handled by a single person.ArtifactRegulatedAug 30, 2026
Action MechanismnounMWEthe operating part that transmits power to a mechanismverifiedMay 18, 2026
Action OfficernounMWEthe case officer designated to perform an act during a clandestine operation (especially in a hostile area)verifiedMay 18, 2026
Action PaintingnounMWEa New York school of painting characterized by freely created abstractionsverifiedMay 18, 2026
action plannounMWESteps that must be taken, or activities that must be performed well, for a strategy to succeed. An action plan has three major elements: (1) Specific tasks: what will be done and by whom. (2) Time horizon: when will it be done. (3) Resource allocation: what specific funds are available for specific activities.ArtifactCUIAug 30, 2026
Action PlantnounMWEprostrate or semi-erect subshrub of tropical America, and AustraliaverifiedMay 18, 2026
Action PotentialnounMWEthe local voltage change across the cell wall as a nerve impulse is transmittedverifiedMay 18, 2026
Action ReplaynounMWEthe immediate rebroadcast of some action (especially sports action) that has been recorded on videotapeverifiedMay 18, 2026
Action SpectrumnounMWEthe efficiency with which electromagnetic radiation produces a photochemical reaction plotted as a function of the wavelength of the radiationverifiedMay 18, 2026
actionable intelligencenounMWEInformation that can be acted upon to address, prevent or mitigate a cyber threat. The sum of an information system’s characteristics in the broad categories (software, hardware, network, processes and human) which allows an attacker to probe, enter, attack or maintain a presence in the system and potentially cause damage to an FMI. A smaller attack surface means that the FMI is less exploitable and an attack less likely.CapabilityRestrictedCUIAug 30, 2026
Activated CarbonnounMWEpowdered or granular carbon used for purifying by adsorptionverifiedMay 18, 2026
Activated CharcoalnounMWEpowdered or granular carbon used for purifying by adsorptionverifiedMay 18, 2026
Activating AgentnounMWE(mineral extraction) a surface-active chemical used in flotation process to increase the attraction to a specific mineralverifiedMay 18, 2026
Activationnounthe activity of causing to have energy and be activeverifiedMay 18, 2026
Activation DatanounMWEPrivate data, other than keys, that are required to access cryptographic modules.DataRegulatedCUIMay 9, 2026
Activation EnergynounMWEthe energy that an atomic system must acquire before a process (such as an emission or reaction) can occurverifiedMay 18, 2026
Activatornoun(biology) any agency bringing about activationverifiedMay 18, 2026
Active AgentnounMWEchemical agent capable of activityverifiedMay 18, 2026
Active Air DefensenounMWEair defense by the use aircraft or missiles or artillery or electronic countermeasuresverifiedMay 18, 2026
Active ApplicationnounMWEan application that is currently running and in the foregroundverifiedMay 18, 2026
active attacknounMWEAn attack on the authentication protocol where the Attacker transmits data to the Claimant, Credential Service Provider, Verifier, or Relying Party. Examples of active attacks include man-in-the-middle, impersonation, and session hijacking.ThreatMay 9, 2026
Active BirthnounMWEchildbirth during which the mother is encouraged to be an active participantverifiedMay 18, 2026
Active CitizennounMWEa citizen who takes an active role in the community (as in crime prevention and neighborhood watch)verifiedMay 18, 2026
active contentnounMWESoftware in various forms that is able to automatically carry out or trigger actions on a computer platform without the intervention of a user.DataAug 30, 2026
active entitynounMWEThe subject role in an access control model — an entity (generally an individual, process, or device) that causes information to flow among objects or changes system state, as opposed to a passive entity that merely contains or receives information. It is distinguished from a passive object by being the initiating party that requests access to an object or the data within an object; it may be a user, program, or process acting to accomplish a task. The field uses the active/passive distinction to anchor access controls — the security features that govern how users and systems communicate and interact with other systems and resources. The contrast class is equally stable: an object (passive entity) contains information and may be a computer, database, file, program, directory, or field in a table.IdentitySep 1, 2026
Active ImmunitynounMWEa form of acquired immunity in which the body produces its own antibodies against disease-causing antigensverifiedMay 18, 2026
Active LearningnounMWEActive learning (also called “query learning,” or sometimes “optimal experimental design” in the statistics literature) is a subfield of machine learning and, more generally, artificial intelligence. The key hypothesis is that, if the learning algorithm is allowed to choose the data from which it learns—to be “curious,” if you will—it will perform better with less training.ProcessAug 28, 2026
Active Learning AgentnounMWE[a machine learning algorithm that can] decide what actions to take [with regards to its training data, in contrast to a passive learning agent, which is limited to a fixed policy].SystemAug 28, 2026
Active Matrix ScreennounMWEa type of LCD screen used for some portable computersverifiedMay 18, 2026
Active PlacebonounMWEa placebo used in experimental tests of a drug that has noticeable side effectsverifiedMay 18, 2026
Active Security TestingnounMWESecurity testing that involves direct interaction with a target, such as sending packets to a target.ProcessAug 30, 2026
Active SitenounMWEthe part of an enzyme or antibody where the chemical reaction occursverifiedMay 18, 2026
Active TransportnounMWEtransport of a substance (as a protein or drug) across a cell membrane against the concentration gradientverifiedMay 18, 2026
Active TrustnounMWEa trust in which the trustee must perform certain dutiesverifiedMay 18, 2026
Active VoicenounMWEthe voice used to indicate that the grammatical subject of the verb is performing the action or causing the happening denoted by the verbverifiedMay 18, 2026